Androgen-ablation is standard therapy for prostate cancer, but this therapy is rarely curative because the cancer within an individual patient contains both androgen-dependent and - independent cells. Several studies have shown an increase in the anti-apoptotic protein Bcl-2 in hormone-independent recurrent prostate cancer, and suggested that groups of prostate cancer cells may resist apoptosis after androgen withdrawal owing to expression of Bcl-2 protein. Approaches to identify novel treatments for recurrent prostate cancer, therefore, should include the development of various strategies that will enable down- regulation of Bcl-2 expression. Our recent studies have identified a novel pro-apoptotic protein designated Prostate Apoptosis Response-4 (Par-4) that can sensitize both androgen-dependent and -independent cells to apoptosis. Most importantly, our preliminary studies suggest that Par-4 down-regulates Bcl-2 protein expression. A goal of this project is to understand the relationship between Par-4 and Bcl-2 expression in androgen-dependent and -independent prostate cancer cell lines, and in tumor specimens representing primary, metastatic, or recurrent prostate cancers. Three specific aims are proposed in this project. Aim I will address the mechanism by which Par-4 down-regulates Bcl-2. Specifically, we will test whether Par-4 causes transcriptional repression of the bcl-2 promoter; and if so, further identify the cis elements in the bcl-2 promoter that mediate the repression. Aim II will examine the functional relevance of Par-4 mediated bcl-2-down-regulation in prostate cancer cells. Finally, Aim III will address the expression of Par-4 and Bcl-2 in hormone-dependent and -independent prostate cancer specimens from patients. We will use qualitative and quantitative approaches to determine whether Par-4 and Bcl-2 expression is inversely related in advanced, metastatic, or recurrent prostate tumors. Together, these studies will enable us to examine the functional link between the pro- apoptotic protein Par-4 and a key cell survival protein Bcl-2, and help design strategies for control of recurrent prostate tumors. Because Bcl-2 blocks diverse insult-induced apoptotic pathways and thereby confers resistance to anti-cancer therapy, the findings of this study can be extended to facilitate apoptosis with Par-4 in diverse cancer model systems.